2 Answers
2

There is quite the nice article at the English Wikipedia on the topic, also explaining the meaning of the term in German.

I was actually right with my guess that the English usage originates in Nietzsche's "Übermensch":

The crossover of the term "über" from German into English goes back to
the work of German philosopher Friedrich Nietzsche. [...] The term was
brought into English by George Bernard Shaw in the title to his 1903
play Man and Superman. During his rise to power, Adolf Hitler
bastardized Nietzsche's term, using it in his descriptions of an Aryan
master race. It was in this context that American Jewish comic book
creator Jerry Siegel encountered the term and conceived the 1933 story
"The Reign of the Super-Man", in which "Superman" is "an evil
mastermind with advanced mental powers".[...] Throughout the following
decade, Siegel, and Joseph Shuster, recast Superman into the iconic
American hero he subsequently became. It is through this association
with Superman the hero that the term "über" carries much of its
English sense implying irresistibility or invincibility.

So there is a very big difference between the usage of those terms in English and German, they're really "false friends".

For some reason, English speakers loaned the word only in its meaning of "overly/very much/too much", and not in the meaning of "across" or "about", but in German usage, there's not really a clear distinction.

I would actually say it comes from Nietzsche's term "Übermensch". It was actually meant as a being "above" the man ("über" also means "above", as in "das Bild hängt über dem Regal") in a more or less evolutionary way. However, it instead got the notion of a "super" kind of man - and a very sad counterpart in "Untermensch". For some reason the English world picked up the "super" notion and use it in this way till today.
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ladybugJul 20 '11 at 13:45

@Ladybug: If you wrote that comment as an answer and elaborated a few bits I'd say it's a pretty acceptable answer.
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Jemus42Jul 21 '11 at 0:30

1

Nietzsche's word Übermensch was also used by the Nazis in their rhetoric about the Herrenrasse (the master race). Further, the opposite term, Untermensch, was used in eugenics. So to the non-native speakers: be very careful when using it. It does have a very dark connotation outside of philosophical circles.
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Stefano PalazzoJul 23 '11 at 14:19